Shaft selection aiding apparatus for selecting optimum shaft for a golfer

ABSTRACT

A high speed camera takes an image in the vicinity of a ball 3 and a club head 12, while a high speed camera 5 takes an image in the vicinity of the top of the swing of a golfer 1, and the images are recorded in a high speed video tape recorder 6. The recorded images are reproduced, swing time, a swing speed and a head speed are detected using a personal computer 15, and a shaft with an optimum flex for the golfer is selected based on the swing time, the swing speed, the swing time and the head speed, or the swing speed and the head speed.

FIELD OF THE INVENTION

The present invention relates generally to an apparatus for selecting ashaft with an optimum flex for a golfer, and more particularly, to anapparatus for selecting an optimum flex for a golfer by which the golfercan select a shaft with a flex the most suitable for him/her.

DESCRIPTION OF THE BACKGROUND ART

Golf clubs having a variety of shaft flexes are available, and a golfermust select a golf club with a flex the most suitable for him/her.Conventionally, an optimum flex for a golfer used to be determined basedonly on a head speed produced from time required for a club head to moveover a fixed distance till impact.

In recent years, as more people enjoy playing golf, some people complainabout their shafts being too stiff or being too flexible. Suchcomplaints do not agree with the head speed standards. Manufactures havechanged their standards into a variety of forms from time to timeaccordingly, but all such new standards are still based on head speedstandards, and other measures have not been taken.

The flex standards described herein are based on frequency values, andstandards based on values representing the tip deflection of a shaftplumped horizontally at the butt end by hanging established weight onthe tip are also encountered with the same problem. The following Table1 sets forth the relation between basic flexes and their frequencies.

                  TABLE 1                                                         ______________________________________                                               Flex Frequency (cpm)                                                   ______________________________________                                               L    235 ± 10                                                              A    245 ± 10                                                              R    260 ± 10                                                              S    275 ± 10                                                              X    290 ± 10                                                              XX   300 ± 10                                                       ______________________________________                                    

The inventors et al. conducted sensory evaluation in which a number ofamateur golfers appreciated items such as "carry distance", "directionalcontrollability", and "readiness of timing" about golf clubs (drivers)with different flexes. As a result, no significant difference was foundabout the two items "carry distance" and "directional controllability",while people supposed to use flexes about in the range from 270 to 280cpm (cycle per minute) with head speeds in the range from 42 to 45 m/secaccording to a conventional selecting method selected shafts whoseflexes vary from 249 to 288 cpm. The inventors et al. therefore came tobelieve that an optimum flex for a golfer cannot be determined basedonly on a head speed.

Note that the swing speeds were also measured at 0.01-second intervalsfrom 0.1 second before till the top of the swing, errors of swing speedsby a number of golfers were smallest at 0.08 second before the top ofthe swing, and therefore swing speeds were limited to those at 0.08second before.

As a result of a study for providing golfers with shafts with optimumflexes, the inventors et al. came to a conclusion that the speed of aclub head at 0.08 second before the top (hereinafter referred to asswing speed) rather than the speed at the top of the swing, i.e., thestate in which the head completely stays still, the amount of strain ofthe shaft at impact, swing time, and acceleration are the most criticalfactors for determining optimum shaft flexes for individual golfers.

It is therefore an essential object of the present invention to providean apparatus for selecting a shaft with an optimum flex for a golferwhich makes it possible for the golfer to find a point the most suitablefor timing or a flex the most comfortable to hit by measuring one ofswing time, swing speed, acceleration and the amount of deflection of ashaft.

DISCLOSURE OF INVENTION

An apparatus for selecting a shaft with an optimum flex for a golferaccording to the present invention detects swing time from the start ofswing till impact, and selects a shaft with an optimum flex for thegolfer based on the detected swing time.

According to another aspect of the invention, the speed of a club headin the vicinity of the top of the swing of the club is detected, and ashaft with an optimum flex for a golfer is selected based on thedetected speed.

According to a further aspect of the invention, the acceleration of aclub head in the vicinity of the top of the swing is detected, and ashaft with an optimum flex for a golfer is selected based on thedetected acceleration of the club head.

According to an additional aspect of the present invention, the movementof a club head in the vicinity of a ball as well as in the vicinity ofthe top of the swing when a golfer swings and hits the ball isvideo-taped, swing time from the start of the swing till impact isdetected based on the video-taped image, the amount of deflection or theamount of strain of the shaft when the golfer swings the golf club andthe hits the ball is measured, the amount of deflection or the amount ofstrain of the shaft at the top of the swing is detected based on thedetected swing time in response to the measurement of deflection amountor strain amount of the shaft, and a shaft with an optimum flex for thegolfer is selected based on the detected output.

According to another additional aspect of the invention, swing time fromthe start of swing till impact and the speed of the club head at impactare detected, and a shaft with an optimum flex for a golfer is selectedbased on the detected swing time and the speed of the club head atimpact.

According to a further aspect of the invention, the speed of a club headin the vicinity of the top of the swing and the speed of the club headat impact are detected, and a shaft with an optimum flex for a golfer isselected based on the detected speed and the speed of the club head atimpact.

According to a still further aspect of the invention, the accelerationof a club head in the vicinity of the top of the swing and the speed ofthe club head at impact are determined, and a shaft with an optimum flexfor a golfer is selected based on the detected acceleration of the clubhead and the speed of the club head at impact.

According to a still further aspect of the invention, the movement of aclub head in the vicinity of a ball when a golfer swings the club andhits the ball as well as in the vicinity of the top of the swing isvideo-taped, swing time from the start of swing till impact is detectedbased on the video-taped image, the deflection amount or strain amountof the shaft when the golfer swings the golf club and hits the ball ismeasured, the deflection amount or the strain amount of the shaft at thetop of the swing is detected based on the detected swing time inresponse to the measurements of the deflection amount or strain amountof the shaft and a shaft with an optimum flex for the golfer is selectedbased on the detected output and the speed of the club head at impact.

According to a further additional aspect of the invention, a shaft withan optimum flex for a golfer is selected based on deflection or strain.

According to a further additional aspect of the invention, the amount ofdeflection or strain of the shaft when a golf ball is hit is detectedusing a strain gauge and thus detected deflection amount or strainamount is counted or expressed by values.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically showing animage-taking/recording system for image-taking/recording the movement ofa club head in a first embodiment of the invention;

FIG. 2 is a block diagram schematically showing a detection device fordetecting swing time and swing speeds;

FIG. 3 is a diagram showing an example of an image displayed in thedisplay shown in FIG. 2;

FIG. 4 is a flow chart for use in illustration of the procedure ofimage-taking/recording by the image-taking/recording system shown inFIG. 1;

FIG. 5 is a flow chart for use in illustration of the procedure ofdetection by the detection device shown in FIG. 2;

FIG. 6 is a view showing the movement of a club head from 0.1 secondbefore the top of the swing till the top of the swing at 0.01-secondintervals;

FIG. 7 is a diagram showing another embodiment of the invention;

FIG. 8 is a chart showing a combined strain waveform according to theembodiment shown in FIG. 7;

FIG. 9 is a flow chart showing the operation of the detection deviceshown In FIG. 7;

FIG. 10 is a graph showing the relations of swing speeds and combinedstrains at top as well as frequencies and values by the sensoryevaluation by a plurality of golfers by first-order approximation.

FIG. 11 is a diagram showing another embodiment of the invention;

FIG. 12 is a graph showing swing speeds in time series;

FIG. 13 is a flow chart showing the procedure of detection according toanother embodiment of the invention;

FIG. 14 is a graph showing the relation between swing speed andacceleration;

FIG. 15 is a diagram showing another embodiment of the invention;

FIG. 16 is a graph showing optimum flex selections produced from swingspeed, head speed and the result of sensory evaluation;

FIG. 17 is a graph showing optimum flex selections produced from theamount of strain at top, head speed and the result of sensoryevaluation;

FIG. 18 is a graph showing optimum flex selections produced from swingtime, head speed and the result of sensory evaluation;

FIG. 19 is a graph showing optimum flex selections produced fromacceleration, head speed and the result of sensory evaluation;

FIG. 20 is a diagram showing another embodiment of the invention.

FIG. 21 is a block diagram specifically showing the structure of theselecting apparatus shown in FIG. 20;

FIG. 22 is an overview showing the selecting apparatus in FIG. 20attached to the grip;

FIGS. 23 and 24 are flow charts for use in illustration of the operationof another embodiment of the present invention; and

FIG. 25 is a graph showing the relation between the amount of strain andtime measured in this embodiment.

BEST MODE FOR PRACTICING THE INVENTION

FIG. 1 is a block diagram schematically showing animage-taking/recording system for image-taking/recording the movement ofa club head in one embodiment of the invention. In FIG. 1, a high speedcamera is placed in order to take the image of a part of a ball 3 fromthe front when a golfer 1 swings a club 2 and hits the ball. A highspeed camera 5 is placed in order to take the image of the top of thehead of golfer 1 from the front. These high speed cameras 4 and 5 whosenumber of frames is 1/200 sec take the images at a time. Video outputsfrom high speed cameras 4 and 5 are recorded by a high speed video taperecorder 6. A metahexa light 7 is provided to illuminate golfer 1 andball 3. Further, in order to strobe-illuminate golfer 1 a strobe light 9is provided, which is activated by a strobe power supply 8 and emitslight in response to pressing of the recording button of high speedvideo tape recorder 6 before golf 1 starts swinging golf club 2.

FIG. 2 is a block diagram schematically showing the detection device fordetecting swing time, swing speed and the speed of a club head atimpact. As shown in FIG. 2, the detection device is formed by aconnection of a personal computer 15, high speed video tape recorder 6shown in FIG. 1, a display 14, a mouse 16, and a printer 17.

FIG. 3 is a diagram showing an image displayed in display 14 shown inFIG. 2. In display 14, the image of golfer 1 taken by high speed camera5 is displayed as an upper half image 11, while the image of ball 3 andclub head 12 taken by high speed camera 4 is displayed as a lower halfimage 10.

FIG. 4 is a flow chart showing the procedure of image-taking/recordingby the image-taking/recording system shown in FIG. 1. FIG. 5 is a flowchart for use in illustration of the procedure of detection by thedetection device shown in FIG. 2, and FIG. 6 is a view showing themovement of a club head 12 from 0.1 second before till the top of theswing.

Now, referring to FIGS. 1 to 6, operations in one embodiment of theinvention will be described. Upon operating the recording button of highspeed video tape recorder 6, recording is initiated and strobe light 9activated by strobe power supply 8 emits light. When golfer 1 swingsgolf club 2, an image in the vicinity of the ball is taken by high speedcamera 4, and an image in vicinity of the top of golfer 1 is taken byhigh speed camera 5, and these images are recorded by high speed videotape recorder 6. When another swinging is video-taped, high speed videotape recorder 6 is stopped temporarily, and the same operation isrepeated once again. When the swinging is over, recording by high speedvideo tape recorder 6 is stopped.

After such images are recorded by high speed video tape recorder 6, thetape is rewound. Then the tape is reproduced, and the images taken bythe image-taking/recording system is displayed in display 14. The tapeis then forwarded frame by frame by JOG/SHATLE to the start of theswing, the time of the start of the swing at which club head 12 startsmoving and the time of impact at which club head 12 hits ball 3 fromimage 10 are detected, and a period of time required from the start ofthe swing till impact, i.e., swing time is detected.

The tape is then rewound and forwarded using the JOG/SHATLE to the point0.1 second before golf club 2 completely stands still over the head inthe swing, in other words 0.1 second before the top of the swing, andhigh speed video tape recorder 6 is stopped at the point. Based on anoriginal calculation program of personal computer 15, mouse 16 moves thecursor on the image displayed in display 14 for digitizing, and variousdata is input to produce a swing speed. FIG. 6 is a view showing themovement of club head 12 until the top of the swing at 0.01-secondintervals.

The tape is then forwarded using JOG/SHATLE and stopped before impact atwhich club 12 hits ball 3. Based on an original calculation program ofpersonal computer 15, mouse 16 moves the cursor displayed in display 14for digitizing, and various data is input to produce a head speed.

The above-described head speed is produced by the image-taking/recordingsystem shown in FIG. 1 and the detection device shown in FIG. 2, but themethod should not be taken limitatively and the head speed can beproduced by using an optical sensor or a magnetic sensor or the like.

The relation shown in the following Table 2 is established between swingspeed and optimum frequency.

                  TABLE 2                                                         ______________________________________                                        Swing Speed  Optimum Frequency (cpm)                                          ______________________________________                                        2.0          250                                                              3.0          269                                                              4.0          278                                                              5.0          281                                                              ______________________________________                                    

The relation in Table 2 is prestored in personal computer 15 so that agolf club whose shaft has an optimum flex for a golfer 1 is selected,the selected club is displayed in display 14, and the result is printedin a printing sheet by a printer 17.

According to the embodiment of the invention, the swing speeds ofindividual golfers are detected, and therefore a golf club having ashaft flex which makes it easiest for each golfer to time or hit can beselected.

In the above-described embodiment, the swinging of golfer 1 isimage-taken using high speed cameras 4 and 5, but the method should notbe taken limitatively, and home video units such as 8 mm video cameraand C-VHS video camera may be used, or the speed in the vicinity of thetop of the swing may be detected using an optical sensor in order todetect a swing speed.

FIG. 7 shows another embodiment of the invention. In this embodiment,the amount of strain of the shaft of golf club 2 during swinging ismeasured, an optimum frequency corresponding to the amount of strain isproduced to select a flex. More specifically, as shown in FIG. 7, singledirection strain gauges 20 are attached at the point 19 located 340 mmfrom the end 18 of golf club 2 along two directions, the direction ofshot and the direction of heels (body) (refer to the cross section),single strain gauges 20 are connected to bridge boxes 21, and strainwaveforms during swinging are output to an FFT analyzer 23 through astrain amplifier 22. The sound of impact between club head 12 and ball 3is collected by a microphone 24 as a sensor trigger input, based onwhich impact time is set to a fixed time point.

FIG. 8 shows an example of a thus measured combined strain waveform. Asshown in FIG. 8, the amount of strain of the shaft is largest in thevicinity of the top while swinging, while golfer 1 can determine best inthe vicinity of the top if the swinging is well timed or not, andtherefore the amount of strain at the top is measured.

FIG. 9 is a flow chart for use in illustration of the operation of thedetection device shown in FIG. 7, and FIG. 10 is a graph showing therelation between swing speeds of a number of golfers and the amounts ofcombined strain at the top for several frequencies as well as the swingspeeds and values produced by sensory evaluations by first-orderapproximation.

As shown in FIG. 9, golf club 2 is brought to a free state, and theamount of strain is set to 0 by strain amplifier 22. When a golferswings golf club 2, the sound of the club hitting the ball is collectedby microphone 24, and input by the sensor trigger. The amount of strainupon swinging golf clubs 2 is detected by single strain gauges 20 andinput to FFT analyzer 23 from bridge boxes 21 through strain amplifier22. It is determined if strain waveform data is taken in normally, andif not, golf club 2 is once again swung. If the data is normally takenin, waveform data is input, the strain waveforms along the twodirections are combined, and the combined strain waveform at the top isdetected. The swing speeds of a plurality of golfers and the combinedstrain amounts at the top for various frequencies as well as the swingspeeds and values produced from the sensory evaluations are expressed byfirst-order approximation in FIG. 10. The first-order approximationstraight lines shown in FIG. 10 are expressed as follows:

    249(cpm):y=354x                                            (1)

    259(cpm):y=331x                                            (2)

    276(cpm):y=290x                                            (3)

    288(cpm):y=246x                                            (4)

Optimum frequency produced from sensory evaluation:

    y=217x+270                                                 (5)

wherein

x: swing speed, and

y: combined strain amount at the top

By applying the expressions (1) to (5), an optimum frequency for eachswing speed can be found by calculation. The relation between the swingspeeds and the optimum frequencies is as in the above Table 2.

Meanwhile, when a ball is hit using a shaft having a certain frequency,an optimum frequency can be found from the amount of strain of the shaftat the top, and values for a shaft having 276 (cpm) are set forth in thefollowing Table 3 by way of example.

                  TABLE 3                                                         ______________________________________                                        Strain Amount at Top (μ ε)                                                          Optimum Frequency (cpm)                                      ______________________________________                                        580              250                                                          870              269                                                          1160             278                                                          1450             281                                                          ______________________________________                                         strain amount at top → strain of shaft with 276 (cpm)             

Note that the swing speed may be replaced with swing time (time from thestart of swinging till impact) or time from the start of swinging tillthe top of the swing. The swing speed described above is produced usingthe image-taking/recording system shown in FIG. 1 and the detectiondevice shown in FIG. 2, but the invention should not be takenlimitatively, and a stop watch, a 8 mm video camera and a C-VHS videotaping system (camcorder, CCD video or the like), or an optical sensorand a magnetic sensor may be used to produce the swing time.

FIG. 11 is a diagram showing an embodiment using the optical sensor. InFIG. 11, a laser type optical sensor 25 is provided under the floorunder the bottom (sole) of club head 12. Before golfer 1 startsswinging, optical sensor 25 illuminates the sole in its ON state, isturned off at the start of swinging, and is once again turned on whenclub head 12 returns to the point for impact. Time from the ON to theON, in other words swing time is output to a counter 26. An optimumfrequency is produced based on the swing time displayed at counter 26.Optimum frequencies for various swing time are set forth in Table 4.

                  TABLE 4                                                         ______________________________________                                        Swing Time (s)                                                                             Optimum Frequency (cpm)                                          ______________________________________                                        1.70         250                                                              1.46         269                                                              1.22         278                                                              0.98         281                                                              ______________________________________                                    

In another embodiment, the acceleration of the head of a golf club from0.1 second before till the top of the swing is found, and an optimumfrequency for each acceleration may be produced. For detection, swingspeeds produced from the detection device shown in FIG. 2 are expressedin a graph in time series, represented by means of first-orderapproximation, and the inclination (negative acceleration) may beproduced. FIG. 12 is a graph showing swing speeds in time series, whileFIG. 13 is a flow chart for use in illustration of the operation ofdetection means in yet another embodiment of the invention. FIG. 14 is agraph showing the relation between swing speed and acceleration.

In this embodiment, as shown in FIG. 13, after input of data, swingspeeds are expressed in a graph in time series, approximated by a linearexpression, and the inclination is produced for comparison with theswing speeds. As shown in FIG. 14, in the relation between swing speedand acceleration the coefficient of correlation is as high as 0.97, andthe swing speed may be replaced with the acceleration. The first-orderapproximation straight line of swing speed and acceleration can beexpressed as follows:

    y=-11.7x+2.7                                               (6)

An optimum frequency can be produced for each acceleration. The relationbetween each acceleration and the optimum frequency is set forth in thefollowing Table 5.

                  TABLE 5                                                         ______________________________________                                        Acceleration (m/s.sup.2)                                                                     Optimum Frequency (cpm)                                        ______________________________________                                        -20.7          250                                                            -32.4          269                                                            -44.1          278                                                            -55.8          281                                                            ______________________________________                                    

The above-described relation between each acceleration and the optimumfrequency is stored in personal computer 15 so that a shaft with anoptimum flex for a golfer can be selected.

FIG. 15 is a diagram showing another embodiment of the invention. InFIG. 15, accelerometer 31 is provided at the head of golf club 2, andthe output of accelerometer 31 is output to an output meter 33 such asoscilloscope and FFT analyzer through a charge amplifier 32. An optimumfrequency is produced based on an acceleration displayed at output meter33.

Lastly, the range of tolerance for swing time, swing speed,acceleration, shaft strain amount at the top, and optimum frequencyfound by experiments based on the invention are set forth in Table 6.

                  TABLE 6                                                         ______________________________________                                                                  Strain Amount of                                                              Shaft at Top (με =                                                 ratio of the amount                                                           of deformation in                                   Swing  Swing              length after force is                                                                     Optimum                                 Time   Speed    Acceleration                                                                            applied and before                                                                        Frequency                               (s)    (m/s)    (m/s.sup.2)                                                                             the force is applied)                                                                     (cpm)                                   ______________________________________                                        1.6 ± 0.1                                                                         2 ± 0.2                                                                             -21 ± 2                                                                               580 ± 50                                                                              250 ± 5                              and more                                                                             and less and less   and less   and less                                1.6 ± 0.1˜                                                                  2 ± 0.2˜                                                                      -21 ± 0.2˜                                                                      580 ± 50˜                                                                       250 ± 5˜                       1.4 ± 0.1                                                                         3 ± 0.2                                                                             -33 ± 2                                                                               870 ± 50                                                                              270 ± 5                              1.4 ± 0.1˜                                                                  3 ± 0.2˜                                                                      -33 ± 2˜                                                                        870 ± 50˜                                                                       270 ± 5˜                       1.2 ± 0.1                                                                         4 ± 0.2                                                                             -44 ± 2                                                                              1160 ± 50                                                                              280 ± 5                              1.2 ± 0.1                                                                         4 ± 0.2                                                                             -44 ± 2                                                                              1160 ± 50                                                                              280 ± 5                              and less                                                                             and more and more   and more   and more                                ______________________________________                                         strain amount at top → strain amount of shaft with 276 (cpm)      

In another embodiment, swing speed and head speed produced using theimage-taking/recording system shown in FIG. 1 and the detection deviceshown in FIG. 2 are considered as items for selecting optimum flexes.

FIG. 16 is a graph showing an embodiment for selecting an optimum flexfound based on a swing speed, a head speed and a result of sensoryevaluation. Note that the sensory evaluation is conducted by means ofpaired comparison test, subjects were selected among advanced players sothat differences between flexes can accurately be evaluated by means ofpaired comparison test.

The straight lines in FIG. 16 are expressed by y=ax+b, wherein

x: swing speed (m/s)

y: head speed (m/s), and

a and b fall within the ranges represented by the following expressions.

    Straight line S1:-6.10≦a≦-4.50 41.5≦b≦46.1(7)

    Straight line S2:-6.10≦a≦-4.50 46.1≦b≦50.7(8)

    Straight line S3:-6.10≦a≦-4.50 59.3≦b≦63.9(9)

    Straight line S4:-6.10≦a≦-4.50 63.9≦b≦68.5(10)

Note that the above straight lines in FIG. 16 are expressed as follows:

    Straight line S1: y=-5.30x+43.8                            (11)

    Straight line S2: y=-5.30x+48.4                            (12)

    Straight line S3: y=-5.30x+61.6                            (13)

    Straight line S4: y=-5.30x+66.2                            (14)

As a result, in the embodiment shown in FIG. 16, detection of the swingspeed and head speed at impact of a golfer makes it possible to select agolf club having a shaft with a flex the easiest to time or hit for thegolfer.

In another embodiment, head speeds and strain amounts at top producedfrom the image-taking/recording system shown in FIG. 1 and the detectiondevices shown in FIGS. 2 and 7 are considered as items for selection ofoptimum flexes.

FIG. 17 is a graph showing an embodiment for selecting an optimum flexbased on a strain amount at top, a head speed and a result of sensoryevaluation. Note that the shaft used had a frequency of 276 (cpm).

The sensory evaluation was conducted by means of paired comparison test,and subjects were selected among advanced players capable of accuratelyevaluating differences between flexes.

The straight lines shown in FIG. 17 are expressed by y=ax+b, wherein

x: shaft strain amount at top (με)

y: head speed (m/s),

and a and b fall within the following ranges:

    Straight line H1: -2.10*10.sup.-2 ≦a≦-1.55*10.sup.-2 41.5≦b≦46.1                                 (15)

    Straight line H2: -2.10*10.sup.-2 ≦a≦-1.55*10.sup.-2 46.1≦b≦50.7                                 (16)

    Straight line H3: -2.10*10.sup.-2 ≦a≦-1.55*10.sup.-2 59.3≦b≦63.9                                 (17)

    Straight line H4: -2.10*10.sup.-2 ≦a≦-1.55*10.sup.-2 63.9≦b≦68.5                                 (18)

Note that in FIG. 17, the above straight lines are expressed by thefollowing expressions.

    Straight line H1: y=-1.83*10.sup.-2 x+43.8                 (19)

    Straight line H2: y=-1.83*10.sup.-2 x+48.4                 (20)

    Straight line H3: y=-1.83*10.sup.-2 x+61.6                 (21)

    Straight line H4: y=-1.83*10.sup.-2 x+66.2                 (22)

Further in another embodiment, swing time and a head speed produced fromthe image-taking/recording system shown in FIG. 1 and the detectiondevice shown in FIG. 2 are considered as selection items for optimumflexes.

FIG. 18 is a graph showing an embodiment for selecting an optimum flexbased on swing time, a head speed and a result of sensory evaluation.Also in this embodiment, the sensory evaluation was conducted by meansof paired comparison test and subjects were selected among advancedplayers capable of accurately evaluating differences between the flexes.

The straight line in FIG. 18 is expressed by y=ax+b, wherein

x: swing time (s)

y: head speed (m/s), and a and b fall within the following ranges:

    Straight line J1: 16.1≦a≦21.8 -7.46≦b≦9.46(23)

    Straight line J2: 16.1≦a≦21.8 -3.54≦b≦14.1(24)

    Straight line J3: 16.1≦a≦21.8 9.66≦b≦27.3(25)

    Straight line J4: 16.1≦a≦21.8 14.3≦b≦31.9(26)

Note that in FIG. 18 the above straight lines are expressed by thefollowing expressions.

    Straight line J1: y=18.9x+0.72                             (27)

    Straight line J2: y=18.9x+5.32                             (28)

    Straight line J3: y=18.9x+18.5                             (29)

    Straight line J4: y=18.9x+23.1                             (30)

Further in another embodiment, an acceleration and a head speed producedfrom the image-taking/recording system shown in FIG. 1 and the detectiondevice shown in FIG. 2 are considered as items for selecting optimumflexes.

FIG. 19 is a graph showing the embodiment for selecting optimum flexesbased on an acceleration, a head speed and a result of-sensoryevaluation. In this embodiment, the sensory evaluation was conducted bymeans of paired comparison test, and subjects were selected amongadvanced players capable of accurately evaluating differences betweenflexes.

The straight lines shown in FIG. 19 are expressed by y=ax+b, wherein

x: acceleration (m/s²)

y: head speed (m/s), and a and b fall within the following ranges:

    Straight line K1: 0.38≦a≦0.51 40.5≦b≦45.4(31)

    Straight line K2: 0.38≦a≦0.51 45.1≦b≦49.9(32)

    Straight line K3: 0.38≦a≦0.51 58.3≦b≦63.2(33)

    Straight line K4: 0.38≦a≦0.51 62.9≦b≦67.8(34)

Note that in FIG. 19 the above straight lines are represented by thefollowing expressions:

    Straight line K1: y=0.44x+42.9                             (35)

    Straight line K2: y=0.44x+47.5                             (36)

    Straight line K3: y=0.44x+60.7                             (37)

    Straight line K4: y=0.44x+65.3                             (38)

FIG. 20 shows another embodiment of the invention. In this embodiment,the maximum strain amount of a shaft when a golfer 30 swings a golf club31 is detected using a strain gauge 34 attached at a position 340 mmfrom a grip end 33, and the detected strain amount is displayed at theindicator of a selecting device 35.

Although strain gauge 34 is attached at the position 340 mm from gripend 33, it is preferable to attach the gauge at a position about 260mm-500 mm from grip end 33 in order to obtain a larger strain value.

Also in this embodiment, the strain gauge was attached in a singledirection along the direction of the body, an additional strain gaugemay be attached in the direction of a shot, and a combined strain amountalong these two directions may be detected.

FIG. 21 is a block diagram specifically showing selecting device 35 inFIG. 20. In FIG. 21, the output of strain gauge 34 is applied toamplifier 41 for amplification, then provided to a 10 Hz low-pass filter42 and removed of its waveform after impact. The output of low-passfilter 42 is applied to an A-D converter 43 and digitized into a digitalsignal to be latched by a data latch 44. The data latched by data latch44 is indicated at a 7-segment indicator 45. The data latched by datalatch 44 is reset in response to an operation of a reset switch 46.

FIG. 22 is an overview showing selecting device 35 attached at the gripshown in FIG. 20. In FIG. 22, 7-segment indicator 45 and reset switch 46are attached on a surface of selecting device 35, and a power supplyswitch 47 is provided on a side. In selecting device 35, amplifier 41,low-pass filter 42, A-D converter 3, data latch 44 and a battery allmounted on a printed circuit board are accommodated, and selectingdevice 35 is attached at grip 31 with a band or the like.

FIGS. 23 and 24 are flow charts for use in illustration of the operationof another embodiment of the invention, and FIG. 25 is a graph showingthe relation between measured strain amount and time in this embodiment.

Referring to FIGS. 21 to 25, the operation of another embodiment will bedescribed. Golfer 30 turns on the power supply operating power supplyswitch 47, confirms if 0 is indicated at 7-segment indicator 45, andoperates reset switch 46 to reset data latch 44 if 0 is not indicated.Golfer 30 then swings golf club 31. Strain gauge 34 outputs a voltagecorresponding to the strain of shaft 32 created by the swinging, thevoltage is amplified by amplifier 41, only a low-frequency component ofthe amplified voltage is extracted by low-pass filter 2, and theextracted component is converted into a digital signal by A-D converter43 to be latched by data latch 44. If data is not normally latched bydata latch 44, golfer 30 operates reset switch 46 to reset data latch44. If data is normally latched by data latch 44, the data is indicatedat 7-segment indicator 45. For another swinging, reset switch 46 isoperated, and power supply switch 47 is turned off upon completion.

Referring to FIG. 24, the operation of indicating data at 7-segmentindicator 45 will be described. Strain is detected by strain gauge 34,the data is latched by data latch 44, and then it is determined if thedata is larger than the previous one. If the strain is larger than theprevious one, it is then determined if the data is above a set value 7.If it is above the set value 7, 7 is indicated at 7-segment indicator.If the data is not above the set value 7, it is then determined if thedata is above a set value 6, and if it is above the value, 6 isindicated. If it is not above the value, it is then determined if thedata is above a set value 5. If the data is above the set value 5, 5 isindicated and if not, it is then determined if the data is above a setvalue 4. If it is above the value, 4 is indicated. If not, it is thendetermined if the data is above a set value 3. If it is above 3, 3 isindicated, and if not, it is then determined if the data is above a setvalue 2. If it is above the value, 2 is indicated, and if not it is thendetermined if the data is above a set value 1. If it is above the value,1 is indicated, and if not 0 is indicated. These values 0 to 7correspond to the strain amounts shown in FIG. 25. More specifically, amaximum value for strain is set to 7, and smaller strains are indicatedby 6, 5, 4, . . . .

Industrial Applicability of the Invention

As in the foregoing, according to the present invention, measuring anyof swing time, swing speed, acceleration and shaft strain for individualgolfers or measuring head speed in addition to these items makes itpossible to select a golf club having a shaft with a flex the easiest totime or hit for each golfer.

What is claimed is:
 1. A shaft selection apparatus for selecting a golfclub shaft having an optimum flex for a golfer, comprising:a selectingunit having a housing attached to the shaft of the golf club, and astrain measurement device within the housing for measuring the amount ofstrain or deflection of the shaft; and a display unit visibly located onthe housing and coupled to the strain measurement device for displayinga numerical value representing the amount of strain or deflectiondetected by the strain measurement device as the golfer swings the golfclub; and a speed detecting unit for detecting the speed of the head ofsaid golf club immediately before impact with a golf ball, whereby thegolfer is enabled to identify a club having an optimum flex based on thenumerically displayed value and the detected speed of the club head. 2.A method for selecting a golf club suitable to the swing of a particulargolfer, comprising:swinging, by the particular golfer, a club havingaffixed thereto a selection unit having a housing enclosing a strainmeasurement device for measuring a strain or deflection amount of theclub as the golfer swings the golf club to the top of a swing; visiblydisplaying at the housing a numerical value representing the maximumamount of strain or deflection detected by the strain measurement deviceduring the swing; measuring the speed of the head of said golf clubimmediately before impact with a golf ball; and selecting a clubsuitable to the particular golfer based at least on the numericallydisplayed value and the measured speed of the club head.